Method of manufacturing an indirectly heated cathode and cathode manufactured according to this method

ABSTRACT

A cathode cap is welded to a metal cylinder over a black sintered metal layer which contains from 60 to 10 percent by weight of metal oxide and which covers the whole cylinder.

United States Patent 19 Van Stratum et al.

[75] Inventors: Antonius Johannes Alberta Van Stratum; Theodorus Hendrikus Weekers, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

7 York, NY.

22 Filed: Nov. 29, 1972 21 Appl. No.: 310,347

[30] Foreign Application Priority Data Dec. 16, 1971 Netherlands 0 7117226 [52] U.S. Cl. 29/2514, 29/484, 313/337 [51] Int. Cl. H0lj 9/00 [58] Field of Search 29/2513, 2514,484, 488,

[ July 16, 1974 [56] References Cited UNITED STATES PATENTS 1,897,933 2/1933 Guthrie et a1 117/49 X 2,726,308 12/1955 Cinamon...

2,970,204 l/1961 Piceu et al..

2,978,606 4/1961 Kahl 3,535,757 10/1970 Nestleroth et a1. 29/25.]4

Primary Examiner-Roy Lake Assistant Examiner-4. W. Davie Attorney, Agent, or Firm-Frank R. Trifari [57 ABSTRACT A cathode cap is welded to a metal cylinder over a black sintered metal layer which contains from 60 to 10 percent by weight of metal oxide and which covers the whole cylinder.

4 Claims, 1 Drawing Figure METHOD or MANUFACTURING AN INDIRECTLY The invention relates to a method of manufacturing an indirectly heated cathode in which a nickel cap as a support of the emissive material is welded to one end of a metal cylinder which is coated with a black layer. The invention furthermore relates to a cathode obtained according to said method.

It is known that a short heating time can be obtained in an indirectly heated cathode consisting of a nickel cap which supports the emitting material and which is welded to a metal cylinder, if the innersurface and the outer surface of the cylinder are coated with a black layer. The black layer on the inside rapidly absorbs thermal energy from the filament, while the black outside radiates much thermal energy at high temperature so that a comparatively large heating energy is required to keep the cathode at the emission temperature. This high thermal energy ensures a short heating time. The

black layer can be obtained in a simple manner by oxidizing the material of the cylinder which usually consists of nickel or of a nickel-chromium alloy, before the cap is provided. l l

The drawback, however, is that the end to which the nickel cap is to be welded must first be'cleaned since welding of the cap to the oxidelayer is not readily possible. This cleaning, however, is time-consuming.

The oxidation after the cap has been welded to the cylinder is disadvantageous since the cap also oxidizes asa result of which the reducerswhich are present in the nickel of the cap are converted into oxides, which produces emission difficulties. 1

I The drawbacks of the said methods can be avoided percent by weight Ni) which is coated with a sintered black layer 2 consisting of 60 percent by weight of tungsten and 40 percent by weight of aluminium oxide.

For that purpose, the surface of the cylinder 1 is dipped in a suspension containing, for example, 2 litres of methylisobutylketonein which 160 g of nitrocellulose have been dissolved and in which 720 g of tungsten powder and 480 g of A1 have been suspended. The layer is then dried and sintered in a hydrogen atmosphere at l,200 C for 60 minutes. The aluminium oxide prevents the fonnation of an alloy between the tungsten and the nickel of thesubstratum which would decrease the radiation of the layer 2. A long cylindrical tube is preferably coated and after sintering cut into parts-of the desired length. A nickel cap 3 is slid over emissive layer 4 is provided on the cap 3. The cap comthe method according to the invention. For example,

if, according to the invention, the cylinder is previously coated with a layer of a suspension comprising one or more suitable refractory metals and one or more metal oxides in powder form, after which the layer is dried and sintered in a reducing atmosphere, the nickel cap is slid over one end of the cylinder coated with the sintered layer and is then welded to said end. Although the sintered layer generally still comprises metal oxide, it has been found that welding does not present any diffi-' culties. Alayer consistingof a mixture of tungsten and aluminium oxide has proved to be very suitable. A layer of molybdenum and aluminium oxide has also proved to be suitable. The quantity of tungsten in the suspension for the layer to be provided may be from 40 to 90 percent by weight, the quantity of aluminium oxide from 60 to 10 percent by weight. However, the suspension may also comprise tungsten or molybdenum and their oxides.

The invention willbe described in greater detail with reference to an embodiment and a drawing the PIO- URE of which is a cross-sectional view through a cathode obtained by meansof the method according to the invention.

Reference numeral 1 in the FIGURE denotes a chromium-nickel cylinder (20 percent by weight Cr, 80

prises strips 5 with nected.

Although in addition to tungsten the layer 2 comprises 40 percent by weight of A1 0 powder, it has beenfound that welding of the cap 3 does not present any difficulties. A heating member is afterwards provided in the cylinder 1. It has been found that the layer 2 maintains a constant black colour throughout the life of the cathode.

Although a single embodiment of a cathode has been described, cathodes which havebeen shaped in a different manner can also be manufactured by means of the cap 3 may be provided with a flange for the connection in the electrode system.

What is claimed is: i

l. A method of manufacturing an indirectly heated cathode, comprising the steps of providing a metal first body and a nickel cap member, coating said metal first body with a layer consisting essentially of at least one refractory metal and at least one metal oxide in powder form, sintering said coated first body in a reducing atmosphere to provide a black layer thereon, and then welding said nickel cap at one end of said coated first body, whereby said nickel cap provides a support for emissive material for said cathode. d

2. A method as claimed in claim 1, wherein said first body is thus coated by dipping in a suspension which consists essentially of from 40 to percent by weight of tungsten and from 60 to 10 percent by weight of aluminum oxide.

3. An indirectly heated cathode, comprising a metal first body coated with a sintered metal layer essentially consisting of from 60 to 10 percent by weight of metal oxide and the balance a metal, further comprising a cap welded to said first body over the sintered layer, and an emissive material provided on said'cap.

4. An indirectly heated cathode as defined in claim 3, wherein said metal is at least one of molybdenum and tungsten and said metal oxide is at least one of aluminum oxide, molybdenum oxide, and tungsten oxide.

which the cathode can be con- 

2. A method as claimed in claim 1, wherein said first body is thus coated by dipping in a suspension which consists essentially of from 40 to 90 percent by weight of tungsten and from 60 to 10 percent by weight of aluminum oxide.
 3. An indirectly heated cathode, comprising a metal first body coated with a sintered metal layer essentially consisting of from 60 to 10 percent by weight of metal oxide and the balance a metal, further comprising a cap welded to said first body over the sintered layer, and an emissive material provided on said cap.
 4. An indirectly heated cathode as defined in claim 3, wherein said metal is at least one of molybdenum and tungsten and said metal oxide is at least one of aluminum oxide, molybdenum oxide, and tungsten oxide. 